Lower Redshift Analogues of the Sources of Reionization

Lower Redshift Analogues of the Sources of Reionization main collaborators: G. Becker, M. Haehnelt (IoA) J.-R. Gauthier, W. Sargent (CIT) M. Rauch (OCIW) Kyoto, May 2012

What are the sources of ionizing photons at the epoch of reionization? Too few QSOs beyond z~4 to maintain ionization of IGM (e.g., Rauch et al 1997) The universe is fully ionized beyond redshift 6 (Becker, Rauch & Sargent 2006) sources are thought to be galaxies: may need to add up light from 10 4 L (at z 8) (e.g., Trenti et al 2010)

How do the photons get out of galaxies? Galactic disks have gas optically thick to ionizing radiation, and are surrounded by optically thick gaseous halos.

Please do not continue to watch if you are easily disturbed by

Please do not continue to watch if you are easily disturbed by explicit guesswork wild speculations unwarranted extrapolations sweeping generalisations

Please do not continue to watch if you are easily disturbed by explicit guesswork wild speculations unwarranted extrapolations sweeping generalisations for my compatriots: brief use of irony

At Low Redshift (z~0): HI ionizing photons cannot get out galaxies (e.g., Hurwitz et al 1997; Deharveng et al 2001; see also poster by Sally Heap) At High Redshift (z ~ 1-3): HI ionizing photons can get out of galaxies (Steidel et al 2001; Shapley et al 2006; Nestor et al 2011) Some HI ionizing photons can get out of some galaxies (e.g., Iwata et al 2009; Inoue et al 2011) No they can t. (e.g., Fernandez-Soto et al 2003; Chen et al 2007; Siana et al 2007,2009; Vanzella et al 2011)

Require favorable circumstances that either increase the production rate of ionizing photons, or ease their escape from the galaxy:

enhanced formation of ionizing photons

enhanced formation of ionizing photons regions of lower opacity, disturbed gaseous halos

enhanced formation of ionizing photons regions of lower opacity, disturbed gaseous halos intra-halo star formation (tidal tails)

Sources at z > 7 are too faint to study the escape of ionizing radiation at the epoch of reionization in any detail. Seek to understand analagous objects at lower redshift (2-3), where we can learn about their nature, gasdynamics, radiative transfer Use Lyalpha emission as a diagnostic. Look for hints of escaping ionizing radiation in ultra-deep surveys for Lya emission

Simple detection strategy for low surface brightness Ly alpha : blind survey with single long slit spectroscopy longslit mask + disperser X t

- Keck LRIS LS spectroscopy of the Hubble Deep Field North - 40 hours on sky 2 GOODS HDFN 60 Lya emitter GOODS

X Faint Ly alpha emitters from ESO VLT-FORS blind survey (92 h): 2-d spectra, 2 x 15 x 1510 km/s wide sources drawn from 5 10 3 L <L obs < 0.2 L dispersion

Most Lyalpha emitters have dominant red emission peaks, spatially compact cores, wide, low SFB halo, are symmetric in the spatial direction. x 120 kpc Lyalpha halo B band continuum Rauch et al 2008 0.020 0.020 flux (a.u.) 0.015 0.010 flux (a.u.) 0.015 0.010 0.005 0.005 0.000 0 2 4 6 8 10 S-N position along slit (arcsec) x 0 2 4 6 8 10 S-N position along slit (arcsec) Not all emitters conform to this pattern, though... 0.000 Consistent with single, central ionizing source!

LDSS3 long slit survey, 61 hours in the HUDF/GOODS S Extended, asymmetric Lyman alpha emitters

x spectroscopically detected extended emitters Ly break galaxies w. Lya emission

10 3 Mpc 3 At a space density of, and fluxes of a few 10 17 erg cm 2 s, 1 the extended,asymmetric objects are more common, and fainter, than Lyman alpha blobs. Surface brightness [erg/cm 2 /s/arcsec 2 ] 2.0 10-17 1.5 10-17 1.0 10-17 5.0 10-18 0-6 -4-2 0 2 4 6 S-N position along slit (arcsec)

Hypothesis: asym., extended Lyman alpha = sites of escaping ionizing radiation Lets look at the three brightest objects...

extended, asymmetric Lyman alpha halo at z~3.049: obscured QSO (V=26.3) apparent Lya dots at the position of two gals? LDSS3 spectrum F606W HST-ACS image fluorescent Lyman alpha?

Inspection of GOODS HST ACS images shows: 2 of the 3 brightest extended Lya emitters corresponds to interacting galaxies! N 1000 km/s E 6" 6" z=3.34 z LDSS3 slit F606W N D B z=2.63 T2 E 10 CA T1 F T1 E LDSS3 F435W F606W

The first object has weird emission in DLA absorption trough: longslit spectrum (61h) w. LDSS3 in the HUDF z~3.444 lyman alpha emitting V~27 galaxy Lyman alpha emission line Lyman alpha forest DLA trough Rauch et al 2011b

emission ridges N "red core" 1000 km/s DLA sits in front of blueshifted, extragalactic gas --> Infall blue, E red, W 5" continuum "blue fan" infalling filament fluoresces in Lyalpha (double-humped profile!) Urbaniak & Wolfe 81 profile FWHM narrower than slit - filament? tilted towards continuum - accelerated infall? Detection of a cold accretion filament? (or in-falling tidal gas?)

view through slit slit view rotated by 90 degs red core N DLA DLA fluorescing filament fluorescing screen S simple double profile likely due to direct impact of ionizing radiation, not rad. transfer of Ly alpha Rauch et al 2011b ~50 % of ionizing photons escape galaxy to hit blue infalling gas stellar ionizing photons account for the entire Lya emission seen.

1000 km/s E N 6" 6" z slit merger may be punching a hole into gaseous halo, or eject a tail with hot stars stripped of gas Escape of ionizing radiation, apparently triggered by interaction. Mergers are more common at high redshift. Is this how the universe gets reionized?

Another extended Lyman alpha halo at z~2.63: z spec =2.63 FG z phot =0.043, 3.06 F435W F606W llongslit spectrum (61h) w. LDSS3 in the HUDF z phot =1.91, 1.49, 2.066 z phot =2.092

Another extended Lyman alpha halo at z~2.63: z spec =2.63 FG z phot =0.043, 3.06 F435W F606W llongslit spectrum (61h) w. LDSS3 in the HUDF z phot =1.91, 1.49, 2.066 z phot =2.092 What is going on with the colors?

Another extended Lyman alpha halo at z~2.63: z spec =2.63 FG 61 h LDSS3 llongslit spectrum (61h) w. LDSS3 in the HUDF F435W F606W introduce young ( (starburst99) 4 10 6 yr) starburst

Another extended Lyman alpha halo at z~2.63: z spec =2.63 61 h LDSS3 llongslit spectrum (61h) w. LDSS3 in the HUDF F435W F606W messy patch of continuum emission (tidal?)

Another extended Lyman alpha halo at z~2.63: z spec =2.63 61 h LDSS3 llongslit spectrum (61h) w. LDSS3 in the HUDF F435W F606W tail of emission terminating in galaxy; B - V = -1.7 could be pure Lyalpha @ 2.2<z<2.9 with rest frame EW ~500-700 A!!!

What could be causing emission from the filament? Need to find astrophysical sources of Lyman alpha emission while producing little continuum light: Fluorescence (hidden AGN) Cooling radiation (cold accretion) Peculiar star formation (hot, metal poor stars)

Lyman alpha cooling radiation from cold accretion: Gas at T=20,000 K and density n = 0.25 cm 3 can produce detected Lyalpha flux of filament through collisional excitation. Equivalent width very high (limited by 2-photon decay only). However, no ionizing radiation produced. Rosdahl & Blaizot 2012

star formation in a turbulent stripped wake (IC3418): Hester et al 2010 relevant for reionization: - young stars, perhaps w. peculiar IMF - fed by metal-poor IGM

star formation in tidal tails: (e.g., Schweizer 1978) Smith et al 2008 Kaviraj et al 2012 relevant for reionization: - young stars, perhaps w. peculiar IMF - potentially fed by metal-poor IGM - stripped partly of HI opacity

Metal-poor, very young stars can produce Lya emission with large Lya EWs. e.g., Kudritzki et al 2000; Tumlinson & Shull 2000; Malhotra & Rhoads 2002, Inoue 2011 This is due to a combination of an enhanced yield of ionizing photons, and departures from case B recombination. Raiter, Schaerer & Fosbury 2010 t Raiter, Schaerer & Fosbury 2010 t Raiter, Schaerer & Fosbury 2010 Lya EW vs. metallicity yield of ionizing photons vs. age

Inoue 2011 z=2.63 filament Z=-3.3 Z=-1.7 remember: mean metallicity of the IGM at z=3: log Z/Z = 2.84 age of the starburst model for main galaxy: 4 10 6 yr estimated EW(Ly ) = 655Å (1 )

NB: These are halos of field galaxies, not clusters! z spec =2.63 FG 61 h LDSS3 llongslit spectrum (61h) w. LDSS3 in the HUDF F435W F606W stellar mass of main galaxy (from Spitzer data) is 10 9 M, total mass is 10 11.6 M,. Should have 2.3 +/- 1.5 subhalos with mass within a decade of mass from the most massive object. Find 5-6. This is a Miky-Way sized halo!

DIfference between extended emitters and Lybreak emitters may be that in the former, satellites are interacting, the latter are currently quiescent.

Conclusions Sources and escape of ionization radiation can be studied at z~3 through ultradeep Lyman alpha emission surveys Inconsistent detections of ionizing radiation from bright (z<4) galaxies may indicate that specific, perhaps transient, conditions required for radiation to escape. Our new observations of extended, asymmetric Lyalpha emitters suggest that interactions are important for the escape of ionizing photons, as they may cause - damage to the gaseous halo - multiple starbursts in satellites - the formation of extragalactic, intra-halo stars (tidal tails, turbulent wakes) - stars to form from the metal-poor IGM/halo gas - a duty cycle (through repeated mergers with finite duration) The increase of the merger rate with redshift makes this process more important when approaching the epoch of reionization -> this may be how reionization happens!